1. Field of the Invention
The present invention relates to flying heads for use with magnetic-drives in computer systems and, more particularly, to an apparatus and method of fabricating a flying-head slider assembly with active control of the head-to-medium clearance in a magnetic disk drive.
2. Description of the Prior Art
In high performance magnetic disk memories of the prior art, the magnetic medium is deposited on a rigid metallic disk, eight to fourteen inches in diameter, and a magnetic transducer is prevented from touching the medium by the so-called "air bearing" effect. The magnetic transducer, also referred to as the "head", is carried by a slider which, in turn, is supported by aerodynamic forces generated by the flow of air between the rotating disk and a plurality of rail-like surfaces on the slider. Such a device is typically embodied in the Winchester technology, as developed by the International Business Machines Corporation in their Model 3340 disk memory. An extensive discussion of magnetic-disk drives is provided by Robert M. White in Disk-Storage Technology, Scientific American, 243, August, 1980, pp. 138-148.
The distance from the magnetic head to the recording surface in a disk system is called flying height because it is the height of the air bearing or slider bottom surface above the disk. The flying height is chosen during system design as a compromise between the features of maximum information density, which requires a small height, and a desire for reliability which requires a large height. Variables in flatness of the disk surface, disk speed variation from inner to outer track, aerodynamic instabilities, resonances of the slider, dust particles, and other factors require that the flying height be increased accordingly to prevent the slider from striking the disk surface or crashing during operations, often resulting in catastrophic destruction of the pickup head and disk surface. At the very least, a crash may cause loss of data bits. A typical compromise for flying height in common use is 20 microinches.
In order to obtain reliable performance at greater bit densities, it is desirable to reduce the height of the head above the disk. For example, a negative-pressure air-bearing suspension system has been reported which allows reducing the flying height to 12 microinches with a 3.5 inch Winchester drive, c.f. Terry Costlow, 3.5-IN. WINCHESTER DRIVE IS QUICK TO EXPLOIT THE LATEST TECHNOLOGIES, Electronic Design, Apr. 28, 1983, p 43.
A structure for laterally displacing a magnetic head on video or audio recording media using a piezoelectric element to align the head with a desired data track, is disclosed in U.S. Pat. No. 4,268,880, Magnetic Head Assembly, issued to Osanu Najima on May 19, 1981. However, the structure shown is not useful for controlling flying head height.
The prior art systems provide little flexibility in controlling flying height, since the various error factors discussed above must all be summed in determining the minimum allowable height. None of the prior art systems has provided apparatus for active closed-loop control of the flying height which would permit closer positional tolerances to be obtained. The present invention provides a means for sensing and dynamically controlling the head to medium height and permits reducing the average disk clearance to as low as 5.+-.1 microinches. Substantially improved reliability and recording density results.